The invention relates to the field of propulsion engines in which a rotor carries swivel-mounted elements.
One type of known propulsion engine that is used in particular in aviation is known as an open rotor or unducted fan engine.
In that type of engine, the rotor carries a plurality of blades that can be swivelled in order to vary their pitch relative to the rotor. Thus, one or more actuators is/are provided for modifying the pitch of the blades. Depending on the pitch that is to be given to the blades and depending on the aerodynamic stresses that are exerted on the blades, the actuator may need to act either as a motor or as a brake.
By way of example, the actuator may be an electric actuator. Under such circumstances, it needs to be supplied with electrical power when it operates as a motor, and it is also necessary to recover the power that it delivers when it operates as a brake.
For this purpose, it is known to use a power supply circuit connecting an electricity source to the actuator. The power supply circuit comprises a direct current (DC) power supply bus and a rectifier/inverter connecting the bus to the actuator. When the actuator operates as a motor, the bus transmits power from the source to the rectifier/inverter, which then operates as an inverter and powers the actuator with an alternating current (AC) voltage. When the actuator operates as a brake, the AC voltage delivered by the actuator is rectified by the rectifier/inverter and dissipated in a dissipation resistance connected to the power supply bus.
That solution presents several drawbacks.
Firstly, the electricity source needs to be dimensioned so as to be capable of delivering the power needed by the actuator when performing a large amplitude motor operation. Typically, the source must for example deliver a peak power of 3300 watts (W). This power is well above the power needed by the actuator for performing small positioning movements on a continuous basis, where that power is typically of the order of 500 W. This high power needs to be transmitted from the stator to the rotor, thereby leading to design constraints.
Furthermore, given the small amount of dissipation resulting from movement of the blades and the high level of efficiency of the actuator, the major part of the power delivered by the source while the actuator is operating as a motor needs to be dissipated in the dissipation resistance while the actuator is operating as a brake. Typically, using the above values, the resistance needs to be capable of dissipating a peak power of 2800 W and a continuous power of 300 W.
Finally, it is known that certification rules applicable to propulsion engines require any electrical system that has an impact on the thrust to be provided in redundant manner. Thus, the source, the power supply bus, the dissipating resistance, and the rectifier/inverter need to be provided in redundant manner. It is therefore necessary to provide two dissipation resistances even though installation constraints may lead to available volumes being relatively small, thereby also having an impact on the size of heat exchangers and/or dissipators.
Document US 2008/0308685 describes a solar powered flying wing having propellers with variable-pitch blades. Nevertheless, that document does not described in detail the motors used for controlling those propellers. In particular, that document does not describe an electrical actuator carried by a rotor of the propellers. Furthermore, the flywheels described in that document are situated inside the structure of the flying wing. Thus, that document does not provide a solution to the high peak power problem that needs to be transmitted from the stator to the rotor in order to power an electrical actuator of a swivel-mounted blade carried by the rotor.
There thus exists at present a need for a solution that enables a swivel-mounted member of an engine rotor to be actuated more efficiently.